Many types of self-propelled agricultural harvesting machines it a chassis, which is provided with driven front wheels and steerable rear wheels. Examples are combine-harvesters and field choppers. A crop attachment for the reception of harvested crop lying or standing on a field is attached on the front end of the chassis of the harvesting machine, with the crop attachment transferring the harvested crop in the harvesting operation to an input conveyor which is connected to the chassis and which is configured in the case of combine-harvesters as a slope conveyor and in the case of field choppers as an input housing. The input conveyor passes the harvested crop into the interior of the chassis, in which harvested crop processing devices, such as threshing, separating and cleaning devices in the case of combine-harvesters and chopping units in the case of field choppers, are arranged.
The crop attachments are usually attached so as to be removable, but otherwise are attached in a rigid manner on the input conveyor. For adaptation to the ground contour, the input conveyor, as a rule, is fastened by means of an actuator so as to be pivotable about an axis extending horizontally and transversely with respect to the forward direction of travel of the chassis of the harvesting machine. A suitable control means detects the height of the crop attachment above the ground by means of a sensor and controls the actuator in such a manner that a desired height or a desired contact pressure of the crop attachment on the ground is achieved. The control means can additionally pivot the crop attachment in relation to the input conveyor about an axis extending horizontally and in the forward direction of the harvesting machine (EP 1 269 823 A1), which, for example in the case of slope combine-harvesters with vertically adjustable wheels for the automatic horizontal alignment of the chassis, is sensible when travelling over slopes. Pivoting the crop attachment automatically about an axis extending horizontally and transversely with respect, to the forward direction in relation to the input conveyor has been proposed (DE 295 19 842 U) in order continually to obtain an optimum outing angle of the combine blades in relation to the harvested crop. Crop attachments which are pivotable in relation to the input conveyor about horizontal axes are consequently known.
In order to reduce the radius of the curve followed by the outer end of the crop attachment and in this way to be able to maneuver the harvesting machine in an easier manner during free cutting of the headland in the corners of a field, or to align the divider of the crop attachment also in curves transversely with respect to the forward direction of the crop attachment, it has been proposed to link the entire crop attachment so as to be pivotable about the vertical axis in relation to the harvesting machine and to drive it in dependence on the steering angle of the harvesting machine (EP 1 808 063 A1 and EP 1 733 608 A1).
Currently there is a need for wider and wider crop attachments. The width of crop attachments not supported separately on the ground, however, is limited by the carrying capacity of the harvesting machine or of the soil under the wheels or caterpillar running gear of the harvesting machine. Harvesting machines with wheels attached on the crop attachment have also certainly been described (U.S. Pat. No. 4,329,833 A1), however it is to be feared that when ground conditions are difficult, such as for example on a slope or where sols are saturated, a harvesting machine of this type with the crop attachment is nevertheless hardly to be moved forward because only the wheels of the harvesting machine are driven and the passively steered (suspended trailing) wheels of the harvesting machine on the slope are, for example, only able to contribute very little to guide the crop attachment along its desired track.